1. Field of the Invention
The present invention relates to a device and a method for guiding a belt-shaped continuous carrier material in an electrographic printer or copier, the carrier material being guided over at least one roller element. The longitudinal axis of the roller element runs substantially transversely to the conveying direction of the carrier material.
2. Description of the Related Art
In electrographic printers and copiers, toner images are often transferred from a toner carrier belt onto a carrier material. The toner carrier belt carries the toner image to be transferred and has a predetermined belt tension. Such toner carrier belts can, for example, be transfer belts for transferring toner images or photoconductor belts for generating toner images. Published PCT Patent Application WO 00/54266 of the same applicant discloses a device for transferring at least one toner image from a toner carrier belt onto a carrier material. The toner carrier belt is guided such that, when a swivel arrangement performs a swivel motion, the belt tension always remains constant.
Published PCT Patent Application WO 01/11432 of the same applicant discloses a method and a controller for the position control of a belt-shaped image carrier in an electrographic printer or copier. The lateral position of the belt-shaped intermediate image carrier is detected at regular intervals by a device-integrated sensor with the aid of a position mark. With the aid of position correcting means, a correction of the position of the intermediate image carrier transverse to the transport direction is implemented corresponding to the detected position and desired position values.
Owing to production variations, circulating toner carrier belts have slightly different lengths and have a slight comicality, or conical shape. However, in the printer or copier, the toner carrier belts must have a defined tensile stress. Published PCT Patent Applications WO 91/11432 and WO 00/54266 disclose devices for length compensation and for conicality compensation. In addition to a tensioning motion in direction of circulation, such an arrangement must also be able to perform a tilting motion of up to approximately xc2x15xc2x0. The tilting motion is required by the conicality of the belt. Up to now, the tilting motion has been realized by an axis mounted in plain bearing""s. Due to the friction of the plain bearings, a tilting motion without jerking is not possible because of the so-called stick-slip-effect. Further, such a mounting has a clearance and has to be additionally fixed in an axial direction. The elements for generating the tilting motion have to be manufactured very precisely in order not to disturb the run of the belt during a tilting motion.
In electrographic printers or copiers, toner carrier belts are guided over several rigidly rollers or over lever mounted deflection rollers, the belt being driven by at least one of these rollers. For this purpose, elements have to be provided that guarantee a constant belt tension and, at the same time, a uniform lateral run of the belt. Further, the possibility that the carrier material may have a conicality has to be taken into account and compensated for. Slight deviations in the parallel alignment of the rollers and a slight conicality of the belt-shaped carrier material already result in force differences between the two belt edges. The belt-shaped carrier material tends to compensate for these force differences, as a result of which the belt drifts, or moves, in a lateral direction. Safe running of the carrier material is thus no longer guaranteed.
In known arrangements, a tensioning device having a roller that presses against the carrier material is provided for the tensioning of the carrier material. The roller of the tensioning device can be tilted orthogonally to its longitudinal axis, i.e. it can be rotated, so that the tension roller can perform a tilting motion imparted by the belt. The components of such a tensioning and tilting device may only have very little manufacturing tolerances. Although an improvement of the belt run can be achieved by means of the known device, such a device for guiding the belt-shaped carrier material is then very expensive und thus not suitable for mass application in printers and copiers.
Another known arrangement provides a further roller that can be tilted relative to the carrier material, in addition to the roller for tensioning the carrier material. In this way, a conicality of the carrier material can be compensated for and forces that result in a lateral drift can be compensated for; however, the angle of tilt has to be determined in a trial run and has to be set. After transport of the printer or copier as well as when the properties of the carrier material change, the angle of tilt has to be re-determined and re-set. Thus, comprehensive setting work is necessary in order to guarantee a safe running of the carrier material.
The present invention provides a device and a method for guiding a belt-shaped continuous carrier material in an electrographic printer or copier, in which a safe running of the carrier material is guaranteed with simple means.
This is achieved in one embodiment by a device for guiding a belt-shaped continuous carrier material in an electrographic printer or copier, having a belt-shaped continuous carrier material that is guided over at least one roller element, the longitudinal axis of the roller element running substantially transversely to the conveying direction of the carrier material during normal operation, at least one rotary arrangement by means of which the roller element can be rotated about a rotational axis running substantially orthogonally to the longitudinal axis, the rotational axis intersecting the carrier material, as viewed in the conveying direction thereof, before the bisector of the circular arc of the roller element that is covered with carrier material.
It is also achieved according to another embodiment by a device for guiding a belt-shaped continuous carrier material in an electrographic printer or copier, having a belt-shaped continuous carrier material that is guided over at least one roller element, a roller support in which the ends of the roller element are mounted, at least one elastic fastener that connects the roller support to the frame such that the roller support can be longitudinally displaced relative to the carrier material and/or transversely tilted relative to the carrier material.
It is further achieved by a method for guiding a belt-shaped continuous carrier material in an electrographic printer or copier, in which a belt-shaped continuous carrier material is guided over at least one roller element, the longitudinal axis of the roller element running substantially transversely to the conveying direction of the carrier material during normal operation, the roller element is rotated by means of at least one rotary arrangement about a rotational axis running substantially orthogonally to the longitudinal axis, and in which the carrier material, as viewed in the conveying direction thereof, is intersected by the rotational axis before the bisector of the circular arc of the roller element that is covered with carrier material.